Elsevier

Ecological Engineering

Volume 52, March 2013, Pages 19-27
Ecological Engineering

Using of activated carbon produced from spent tea leaves for the removal of malachite green from aqueous solution

https://doi.org/10.1016/j.ecoleng.2012.12.032Get rights and content

Abstract

Spent tea leaves, as a waste material, were used to produce active carbon (STAC) in this study. STAC was used as low-cost adsorbent to remove malachite green (MG) from aqueous solutions. Characterization of STAC was made by using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and surface area measurements. The effects of contact time, pH, temperature, amount of adsorbent and ionic strength on removal of malachite green were investigated. The STAC exhibited largest adsorption capacity (256.4 mg g−1) at 45 °C. STAC removed 94% of malachite green from aqueous solution and adsorption is favorable at operation conditions studied. The amount of adsorbed malachite green increased up to pH 4 and remained constant above the pH 4. Equilibrium sorption data were analyzed by Freundlich, Langmuir and Dubinin–Radushkevich equations. Langmuir isotherm exhibited the best fit with the experimental data. Sorption kinetics was determined by pseudo-first-order, pseudo-second-order, Elovich rate equations and intraparticle diffusion models. The adsorption of MG onto STAC followed pseudo-second-order kinetics. From the thermodynamic studies, the negative value of free energy (ΔG°) and positive value of enthalpy (ΔH°) changes indicated the spontaneous and endothermic nature of the adsorption.

Introduction

Synthetic dyes are mostly used in many industries such as textile, leather tanning, paper production, food technology and hair colorings. Wastewaters from these industries are usually polluted by dyes. Malachite green (MG) is most commonly used for the dyeing of cotton, silk, paper, leather and also in manufacturing of paints and printing inks. Malachite green is widely used in distilleries for coloring purposes (Khattri and Singh, 1999a). Recent investigations show that such a substance is linked to an increased risk of cancer. MG is highly cytotoxic to mammalian cells and also acts as a liver tumor-enhancing agent (Rao, 1995).

Various studies have been made to remove MG from the wastewater. A lot of adsorbent materials were used to remove MG from the wastewater. One of these adsorbent is active carbon (Hameed et al., 2007a, Hameed et al., 2007b, Tan et al., 2007, Tan et al., 2008, Hameed and Daud, 2008). Previously, a number of low cost materials including activated slag (Khattri and Singh, 1999a), sugar cane dust (Khattri and Singh, 1999b), sagaun sawdust (Khattri and Singh, 2000), neem sawdust (An et al., 2002), citrobacter sp. (Guo et al., 2003a), rice husk-based active carbon (Garg et al., 2003), formaldehyde treated and sulphuric acid treated saw dusts (Janos et al., 2003), fly ash (Khan et al., 2004), coal (Garg et al., 2004), prosopis cineraria sawdust (Janos, 2003), iron humate (Guo et al., 2003b), perennial weed (Sivaraj and Subburam, 2002), maize cob (Jose et al., 2000), combination of chitin with activated charcoal and alumina (Shukla and Singh, 1999), bentonite, sepiolite and zeolite (Inel and Askin, 1996), and a carbonaceous sorbent prepared from an indigenous agricultural waste, jack fruit peel (Inbaraj and Sulochana, 2002) have been shown to be successful sorbent materials for the removal of malachite green from aqueous solutions (Kumar et al., 2005). Gupta and Ali (2002) have reviewed low-cost adsorbents to remove various pollutants including dyes.

Tea is basically dried and processed leaves of only one species of plant called Camellia sinensis (Mokgalaka et al., 2004). It is consumed by the most of people in the world and is the second most popular beverage in the world. It is estimated that somewhere between 18 and 20 billion cups of tea are drunk daily on world. Producers face a problem in disposing of spent tea leaves after extraction. Hence, the utilization of such waste is important (Hameed, 2009).

The aim of this study is to produce active carbon from spent tea leaves (STAC) which was activated with NaOH, 4% solution. STAC has been used for the removal of malachite green from aqueous solution. In this study effects of pH, temperature, amount of adsorbent and ionic strength were investigated. Thermodynamic and kinetic parameters have also been investigated.

Section snippets

Material

MG was purchased from Carlo Erba. Its chemical formula and molecular weight are C23H25ClN2 and 364.90 g/mol, respectively. HCl and NaOH were obtained from Riedel-de Haen.

Preparation of activated carbon from spent tea leaves (STAC)

Spent tea leaves were obtained by using black tea supplied from Çaykur, Turkey. After washing process by using distilled water, tea leaves were oven-dried at 80 °C for 2 h. The dried samples were ground in a laboratory blender and sieved to particles <210 μm. The resulting spent tea leaves samples were added into 200 mL NaOH of 4%

Surface properties

The N2 adsorption isotherms of both untreated carbon and STAC at 77 K are given in Fig. 1. STAC exhibits typical type II isotherm, which is generally referred to as sigmoid isotherm or S type isotherm (Rouquerol et al., 1999, Erbas et al., 2005). Physical adsorption on STAC can accomplish type II isotherm, and correspond to multilayer formation (Adamson, 1990, Erbas et al., 2005). Type II isotherm data were evaluated through BET area, cumulative adsorption surface area by DH method, external

Conclusion

We have come to the conclusion that active carbon obtained from spent tea leaves can be used as efficient low-cost adsorbent for the removal of malachite green from aqueous solutions. In spite of low BET surface area of activated carbon fabricated in this study, it exhibits considerably greater sorption capacity to malachite green. Adsorption of malachite green from aqueous solution onto STAC was investigated by various parameters such as pH, temperature, amount of adsorbent and ionic strength.

Acknowledgements

We would like to express our gratitude to Berke Özdağ and Fatma Ezgi Saygın for their contributions to our study.

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